Impeller for axial or radial flow compressors



0a. 27, 1910 STIEFEL ETAL 3,536,417

IMPELLER FOR AXIAL OR RADIAL FLOW COMPRESSORS Original Filed Sept. 19,1966 2 Sheets-Sheet 1 WALTER STIEFEL Y HANS MERKLE INVENTORS BY (QM-wATTORNEYS Oct. 27,1970 W.$T|EFEL EI'AL 3,536,417

IMPELLER FOR AXIAL OR RADIAL FLOW COMPRESSORS Original Filed Sept. 19,1966 2 Sheets-Sheet 2 WALTER STIEFEL HANS MERKLE mvsu roas BY M9ATTORNEYS United States Patent O 3,536,417 IMPELLER FOR AXIAL R RADIALFLOW COMPRESSORS Walter Stiefel, Neuhausen, and Hans Merkle, Stuttgart-Frauenkopf, Germany, assignors to Daimler-Benz Aktiengesellschaft,Stuttgart-Unterturkheim, Germany Continuation of application Ser. No.580,450, Sept. .19, 1966. This application Jan. 30, 1969, Ser. No.800,336 Claims priority, applicfitigg Gfielrmany, Sept. 22, 1965,

Int. Cl. F04d 19/00, 29/26 US. Cl. 416--223 4 Claims ABSTRACT OF THEDISCLOSURE This application is a continuation of application Ser. No.580,450, filed Sept. 19, 1966, now abandoned.

BACKGROUND OF THE INVENTION A burbling phenomenon, called rotatingstall, occurs at the blades of such compressors-at the rotors as well asat the stators thereofwithin a certain speed range of the engine. Thisphenomenon is the consequence of a lessening of the amount of flowthrough the compressor, or an increase in the angle of incidence of theflow on the blades of the compressor and can be considered a preliminarystage of the simultaneous stalling at all blades, known as pumping.However, in contradistinction to pumping, the rotating stall involvesstalling at individual blades, and such stalling phenomena can betriggered, at a certain critical magnitude of the angles of incidence,by normal irregularities within the fluid flow. These stallingphenomena, so to speak, result from a damming up of flow at the entranceto the compressor, and a rotating of the fluid therein at a frequencywhich differs from the frequency of the speed of rotation of the rotor.As a result, this phenomenon is called rotating stall. As a consequenceof the pressures created by this effect, blade vibrations and bladebreaks can occur, and for this reason, it was heretofore necessary toavoid speeds of rotation or flow quantity located in the vicinity of thecritical surge limit, for safety reasons. However, by taking suchprecautionary measures, the flexibility in speed of rotation or volumeof flow of the compressor is substantially impaired.

SUMMARY OF THE INVENTION The present invention is intended to solve theproblems of avoiding the above-described disadvantage without having tofulfill the restrictive conditions set out above. In order to solve thisproblem, the invention starts with the general objective to prevent theoccurrence of the rotating stall by intentionally providingirregularities in the blade construction of the impeller. In detail, theinvention proposes to make individual blades or blade groups deviatefrom the other blades of the rotor with respect to shape and/ orposition. This inventive idea can also be put into practice by providingcertain blades or groups of blades with a blade angle deviating fromthat of the remaining blades, and/or by providing them with a differentbasic 3,536,417 Patented Oct. 27, 1970 shape, and/ or by making thepitch of the rotor different. The individual features of the inventioncan thus be em ployed in combination, in certain individual groupings,or each feature may be utilized by itself.

By means of the above-disclosed inventive concept, there is obtained adifferentiation or shift of the fluid flow from laminar to turbulentflow at the individual blades. If, for example, the phenomenon of thisinterruption of laminar flow occurs at a blade, and the interruptionbegins to rotate, it then meets with one or several blades having adifferent shape and/ or position, and thus the fiuid'fiow isadvantageously made to engage the blade again. Depending upon the type,number, and magnitude of the irregularities, areas of flow interruptioncan be completely eliminated, weakened, prevented from rotating, or atleast shifted into zones of smaller through flow and different speeds ofrotation.

The measures of the invention can, in principle, be provided at anydesired location along the circumference of the impeller. However, it isadvantageous, particularly in the case of rotors, to make suchprovisions at opposite or symmetrical points at the diameter of theimpeller, in order to avoid imbalances and a concomitant irregular runof the impeller. Thus, in case of an even number of blades, it would bepossible, for example, to arrange and/or construct every second blade ina different manner, according to the invention. Of course, it islikewise possible, and definitely within the scope of the invention, toprovide the irregularities at random blades and subsequently by othermeans provide an accurate balancing of the impeller.

The above-mentioned dilferent shaping or positioning of individualblades or groups of blades can, basically, be effected in any desiredmanner. A main consideration, in this connection, is a change in theblade angle. For this purpose, the invention proposes to provideindividual blades or blade groups with a different inlet angle from theremaining blades. This can be done, for example, in such a way that therespective blades are bent somewhat at their roots and thus the inletangle is reduced in comparison to that of the other blades. However,according to the invention, it is preferred to fashion these individualblades or the blade groups in such a way that they are moved up, orconventionally, cut back at the root. It is also possible to impart tosuch blades a different curvature at the root area.

In this manner, it is advantageously possible, for example in case ofcutback blades, to manufacture all blades identically and then, as afinishing operation, to subject individual blades to this cut-backprocedure. As mentioned above, it is advantageous, for example, in orderto render flow interruption ineffective as quickly as possible, andpreferably at the very next blade, to cut back alternately every secondblade. Although it is known to cut back every second blade, this measureheretofore had the purpose of increasing the flow through thecompressor. The blades, in the known case, must be cut back beyond thenarrowest cross section, while, in accordance with the presentinvention, the cutting back of the blades is intended to change theangle of flow and has no relationship whatsoever to the narrowest crosssection, i.e., the cutback does not have to be beyond such crosssection.

Another embodiment of the invention, likewise relating to the variationin individual angles of incidence (stagger angles), provdes thatindividual blades or blade groups have a different basic shape.Sometimes, it is suflicient to provide an increase in the relativethickness and/or a thickening at the entrance (root) portion of theselect blades. Finally, it is also possible to utilize a variation inthe postionng of the blade for changng the angle of incidence. For thispurpose, according to the invention,

3 individual blades or groups thereof are provided on the impeller sothat they are twisted about their radially extending axis with respectto the other blades. Here, again, all blades can be identicallymanufactured and must only be attached to the impeller body in varyingpositions.

According to the invention, another positional change can be provided byarranging individual blades or blade groups at a different pitch alongthe impeller. This measure per se is conventional, for example, inhydrodynamic clutches, but there it serves for entirely differentpurposes, namely, for preventing a coincident blow or knock in theclutch.

It is an object of the present invention to provide an impeller forcompressors, particularly for use in aircraft engines, which avoids orotherwise completely eliminates the inherent probems relating toso-called rotating stall in known arrangements.

It is another object of the present invention to solve theabovementioned problems of the prior art in a relatively simple andeconomical manner.

It is a further object of the present invention to prevent theoccurrence of rotating stall by intentionally providing irregularitiesin the blade construction of the impeller so as to dissolveinterruptions in the laminar fluid flow therethrough.

It is another object of the present invention to provide an impellerwherein individual blades or blade groups deviate from the other bladesof the rotor with respect to shape or position so as to eliminate asquickly as possible rotating irregularities in the laminar fluid flow.

BRIEF DESCRIPTION OF THE DRAWING These and other objects, features andadvantages of the present invention will become clearer from thefollowing detailed description thereof when taken in connection with theaccompanying drawings, which illustrate several embodiments of theinvention, and wherein:

FIGS. 1, 2 and 4 show various embodiments of blade arrangementsaccording to the invention in a schematic view; and

FIG. 3 shows an impeller of a radial flow compressor having a bladearrangement according to FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings,wherein like reference numerals are utilized throughout the severalviews to designate corresponding parts wherever possible, andparticularly to FIG. 1, blades 10 and 11 form a cascade of bladeswherein certain blades, for example, the alternate blades 11, are of astronger curvature at the root 12 than the blades 10 and thus areprovided with a larger entrance angle than the blades 10. The dot-dashline 13 at the blades 11 indicates the shape of all other blades 10.There is thus obtained with respect to a given fiow direction, adifferent angle of incidence (stagger angle) at the blades 11, so thatthe effect of generating irregularities in the fluid fiow at theseblades according to the invention is achieved.

The same efiect as in the embodiment of FIG. 1 may be obtained by theembodiment of FIG. 2. In this figure, every second blade 11a is cut backin length at the root 12 with respect to the normal blades 10. Thisembodiment is also shown in FIG. 3, wherein there is illustrated in sideview an impeller 14 of a radial flow compressor of basically known type.This embodiment of FIG. 3 has the advantage that the blades 10 and 11acan be manufactured identically. Cutting back every second blade 11a canthen be conducted as a finishing step.

In the embodiment of FIG. 4, a varying angle of incidence is obtained byrotating every second blade 11b about its radial axis.

The dot-dash line 15 corresponds to the position of all other blades 10.Thus, the blades 10 and 1112 can be of identical configuration; theyneed only be attached at the impeller body in varying positions toattain the objectives of the present invention.

While we have shown and described several embodiments in accordance withthe present invention, it is understood that the sarne is not limitedthereto, but is susceptible of numerous changes and modifications asknown to a person skilled in the art, and we therefore do not wish to belimited to the details shown and decsribed herein; but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

What is claimed is:

1. A compressor impeller having a plurality of blades mounted adjacentto one another in a substantially annular array with their leading andtrailing edges being respectively annularly aligned in common planes andwith some of the blades exhibiting a different characteristic from thatof the remaining blades of the array to resist the formation of rotatingstall, wherein the improvement comprises each of some of said blades ofthe array having their leading edge portions inclined in the samedirection as the remaining blades, with respect to a plane passingthrough the axis of the impeller and its longitudinal axis, but to agreater extent, thus defining larger inlet angles than said remainigblades, wherein all of said blades have substantially identical trailingedge portions.

2. The compressor impeller according to claim 1, wherein. all of saidblades have substantially identical cross-sections except for only theleading edge portions of said some of the blades having a greatercurvature to form their larger inlet angles.

3. The compressor impeller according to claim 1, wherein said some ofthe blades and said remaining blades alternate in the annular array.

4. The compressor impeller according to claim 1, wherein all of saidblades have substantially identical cross-sections except for only theleading edge portions of said some of the blades having a greatercurvature to form their larger inlet angles.

References Cited UNITED STATES PATENTS 1,087,995 2/1914 Sturtevant230134.5 1,534,721 4/1925 Lasche 25339 1,639,274 8/1927 Zoelly et a1.25377 1,893,184 1/1933 Smellie 230-134 2,570,155 10/1951 Redding 253772,798,661 7/1957 \Villenbruck et al. 230122 2,870,958 1/1959 Pinsley253-77 3,347,520 10/1967 Owezov 25377 FOREIGN PATENTS 83,294 6/ 1920Austria.

685,979 12/1939 Germany.

830,542 2/ 1952. Germany. 1,177,277 9/1964 Germany.

HENRY F. RADUAZO, Primary Examiner U.S. Cl X.R. 230l20

